Method and apparatus for transmission/reception of D2D signal

ABSTRACT

A method and apparatus for supporting a device-to-device (D2D) communication between user equipments (UEs) are provided. The method of a device-to-device (D2D) communication between user equipments (UEs), the method includes: receiving, at a transmission (Tx) UE, resource assignment information transmitted from an evolved NodeB (eNB), the resource assignment information being associated with a D2D discovery signal to be transmitted in a discovery period; determining, at the Tx UE, that a D2D discovery signal associated with a first discovery type and a D2D discovery signal associated with a second discovery type are to be transmitted in a first subframe included in the discovery period; and in the first subframe, transmitting the D2D discovery signal associated with the second discovery type and dropping the D2D discovery signal associated with the first discovery type.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority from and the benefit of Korean PatentApplication Nos. 10-2014-0102675, filed on Aug. 8, 2014, and10-2014-0162802, filed on Nov. 20, 2014, all of which are herebyincorporated by reference in its entirety.

BACKGROUND

1. Field

The present disclosure relates to wireless communication and, moreparticularly, to a method and apparatus for transmitting and receiving aDevice-to-Device (D2D) signal.

2. Discussion of the Background

Long Term Evolution (LTE) of 3^(rd) Generation Partnership Project(3GPP) allows supporting a Proximity Service (ProSe) so as to satisfydemands associated with public safety. As a discovery technology andbroadcasting communication are added to the ProSe, there is a desire fora technology for providing compatibility in an LTE system.

Device-to-device (D2D) communication relates to a communication methodhaving been available since the era of an analog two-way radio and hasbeen used over the very long history. However, D2D communication in awireless communication system is distinguished from existing D2Dcommunication.

The D2D communication in the wireless communication system indicatescommunication that uses a transmission and reception technology, forexample, a physical channel, of the wireless communication system in afrequency band of the wireless communication system or a band excludingthe frequency band, and in this instance, enables user data to bedirectly transmitted and received between devices, for example, userequipments (UEs), without using an infrastructure, for example, anevolved-NodeB (eNB). That is, two UEs function as a source and adestination of data, respectively, and perform communication. Such amethod enables wireless communication to be available in an area outsidea limited wireless communication infrastructure and also decreasesnetwork load of the wireless communication system.

The D2D communication may be performed through a communication method ofusing an unlicensed band of a wireless local area network (WLAN), suchas Institute of Electrical and Electronics Engineers (IEEE) 802.11, orBluetooth. However, the communication method using the unlicensed bandmay not readily provide a planned and controlled service. In particular,performance may be significantly degraded due to interference. On theother hand, D2D communication operated or provided in a licensed band oran inter-system interference controlled environment may support therelatively high quality of service (QoS), may improve the frequency useefficiency through a frequency reuse, and may also increase acommunicable distance.

In the case of D2D communication using the licensed band, that is, D2Dcommunication based on cellular communication, resources for D2Dcommunication may be allocated through an eNB. For example, cellularuplink (UL) channels or UL subframes may be used as resources to beallocated. The D2D communication includes D2D data communication and D2Dcontrol signal communication. Unlike cellular communications, the D2Dcommunication may be performed without a control by a network. Thus, aplurality of D2D signals may be overlapped in the same time with respectto a UE, for example, a collision of the plurality of D2D signals mayoccur. Accordingly, there is a need to prevent and/or resolve such aproblem.

Also, a User Equipment (UE) having a single transceiver chain isincapable of executing simultaneous transmissions/receptions throughvarious frequency bands. Accordingly, for effective D2D communication ina licensed band, there is a need of assigning a priority a signal forprocessing D2D signals when a collision occurs among the D2D signals.

SUMMARY

Exemplary embodiments relate to a method and apparatus for transmittingand receiving a Device-to-Device (D2D) signal.

Exemplary embodiments also relate to a method and apparatus fordetermining priority for a Device-to-Device (D2D) signal.

Exemplary embodiments also relate to a method and apparatus fortransmitting and receiving a Device-to-Device (D2D) signal based onpriority.

Exemplary embodiments also relate to a method and apparatus forprohibiting collision among Device-to-Device (D2D) signal based onpriority.

An exemplary embodiment discloses a method of a device-to-device (D2D)communication between user equipments (UEs), the method including:receiving, at a transmission (Tx) UE, resource assignment informationtransmitted from an evolved NodeB (eNB), the resource assignmentinformation being associated with a D2D discovery signal to betransmitted in a discovery period; determining, at the Tx UE, that a D2Ddiscovery signal associated with a first discovery type and a D2Ddiscovery signal associated with a second discovery type are to betransmitted in a first subframe included in the discovery period; and inthe first subframe, transmitting the D2D discovery signal associatedwith the second discovery type and dropping the D2D discovery signalassociated with the first discovery type.

An exemplary embodiment discloses a transmission (Tx) user equipment(UE) to execute a device-to-device (D2D) communication with a reception(Rx) UE, the Tx UE including: a wireless transceiver configured toreceive resource assignment information transmitted from an evolvedNodeB (eNB), the resource assignment information being associated with aD2D discovery signal to be transmitted in a discovery period, andtransmit a D2D discovery signal to a Rx UE; and one or more processorsconfigured to determine that a D2D discovery signal associated with afirst discovery type and a D2D discovery signal associated with a seconddiscovery type are to be transmitted in a first subframe included in thediscovery period, and in the first subframe, transmit the D2D discoverysignal associated with the second discovery type and drop the D2Ddiscovery signal associated with the first discovery type.

An exemplary embodiment discloses a method of a device-to-device (D2D)communication between user equipments (UEs), the method including:receiving configuration information for a D2D communication from anevolved NodeB (eNB); receiving, at a transmission (Tx) UE, informationof a resource pool transmitted from the eNB, the information of theresource pool being associated with a first D2D discovery signaltransmission; receiving, at the Tx Ue, discovery resource informationassociated with a second D2D discovery signal transmission, thediscovery resource information indicating a specific resource for thesecond D2D discovery signal transmission; determining the second D2Ddiscovery signal transmission through the specific resource, thespecific resource including a first subframe and a second subframe;determining the first D2D discovery signal transmission through aresource selected from the resource pool, the selected resourceincluding the second subframe and a third subframe; and executing thesecond D2D discovery signal transmission in the second subframe, anddropping the first D2D discovery signal transmission in the secondsubframe.

According to one or more exemplary embodiments, when a collision occursamong D2D signals, a User Equipment (UE) may execute transmission andreception of a D2D signal based on a priority, and efficiency of D2Ddiscovery and D2D communication may be generally secured.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating a wireless communication systemaccording to one or more exemplary embodiment.

FIG. 2 and FIG. 3 are diagrams schematically illustrating a structure ofa Radio Frame (RF) according to one or more exemplary embodiments.

FIG. 4 illustrates an example of D2D communication based on a cellularnetwork according to one or more exemplary embodiments.

FIG. 5 is a diagram illustrating an example of a D2D discovery resourceaccording to one or more exemplary embodiments.

FIG. 6 is a diagram illustrating an example of a D2D discovery resourceset according to one or more exemplary embodiments.

FIG. 7 is a diagram illustrating examples of a D2D discovery resourceconfiguration structure in a D2D discovery resource set according to oneor more exemplary embodiments.

FIG. 8 to FIG. 12 are diagrams illustrating delivery of informationamong user equipments (UEs) and a base station (BS), for D2Dcommunication, according to one or more exemplary embodiments.

FIG. 13 illustrates an example of a potential collision among D2Dsignals.

FIG. 14 illustrates another example of a potential collision among D2Dsignals.

FIG. 15 is a flowchart illustrating operations of a User Equipment (UE)according to one or more exemplary embodiments.

FIG. 16 is an example of a block diagram illustrating a UE according toone or more exemplary embodiments.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

Exemplary embodiments will be described more fully hereinafter withreference to the accompanying drawings, in which exemplary embodimentsof inventive concept are shown. Throughout the drawings and the detaileddescription, unless otherwise described, the same drawing referencenumerals are understood to refer to the same elements, features, andstructures. In describing the exemplary embodiments, detaileddescription on known configurations or functions may be omitted forclarity and conciseness.

Further, the terms, such as first, second, A, B, (a), (b), and the likemay be used herein to describe elements in the description herein. Theterms are used to distinguish one element from another element. Thus,the terms do not limit the element, an arrangement order, a sequence orthe like. It will be understood that when an element is referred to asbeing “on”, “connected to” or “coupled to” another element, it can bedirectly on, connected or coupled to the other element or interveningelements may be present.

Several aspects of telecommunication systems will be described withreference to various apparatuses and methods. Various blocks, modules,components, circuits, steps, processes, algorithms, operations, etc.(collectively referred to as “elements”) will be described withreferences to various apparatuses and methods. These elements may beimplemented using electronic hardware, computer software, or anycombination thereof.

For example, an element, or any portion of an element, or anycombination of elements may be implemented with a processing system thatincludes one or more processors. Examples of processors includemicroprocessors, microcontrollers, digital signal processors (DSPs),field programmable gate arrays (FPGAs), programmable logic devices(PLDs), state machines, gated logic, discrete hardware circuits, andother suitable hardware configured to perform the various operationsdescribed throughout this disclosure. One or more processors in theprocessing system may execute software. Software shall be construedbroadly to mean instructions, instruction sets, code, code segments,program code, programs, subprograms, software modules, applications,software applications, software packages, routines, subroutines,objects, executables, threads of execution, procedures, functions, etc.,whether referred to as software, firmware, middleware, microcode, orotherwise.

In one or more exemplary embodiments, the operations and/or functionsdescribed may be implemented in hardware, software, firmware, or anycombination thereof. If implemented in software, the operations and/orfunctions may be stored on or encoded as one or more instructions orcode on a computer-readable medium. Computer-readable storage medium mayinclude non-transitory storage media. The storage media may be anyavailable media that can be accessed by a computer. For example, thestorage media may include Random Access Memory (RAM), Read-Only Memory(ROM), EEPROM, CD-ROM, or other optical disk storage, magnetic diskstorage or other magnetic storage devices, or any other medium that canbe used to carry or store desired program code in the form ofinstructions or data structures and that can be accessed by a computer.However, types of computer-readable medium are not limited thereto.

FIG. 1 illustrates a wireless communication system according to one ormore exemplary embodiments.

Referring to FIG. 1, the wireless communication system 10 is widelylocated to provide a variety of communication services such as a voiceservice and a packet data service. The wireless communication system 10includes one or more evolved-NodeBs (eNBs) 11. Each eNB 11 provides acommunication service to a predetermined cell, for example, cells 15 a,15 b, and 15 c. Here, the cell may be divided into a plurality of areas(also, referred to as sectors).

User equipment 12 (UE) may be located at a certain location or portable,and may also be referred to as different terms, including MS (mobilestation), MT (mobile terminal), UT (user terminal), SS (subscriberstation), wireless device, PDA (personal digital assistant), wirelessmodem, and handheld device. An eNB 11 may also be referred to as BS(Base Station), BTS (Base Transceiver System), Access Point, femto basestation, Home nodeB, relay and the like. A cell inclusively refers tovarious coverage areas, such as mega cell, macro cell, micro cell, picocell, and femto cell. A cell may be used as a term for indicating afrequency band that a BS provides, a coverage of a BS, or a BS.

Hereinafter, the term downlink refers to communication from a basestation 11 to a UE 12, and the term uplink refers to communication froma UE 12 to a base station 11. For downlink, a transmitter may be part ofa base station 11, and a receiver may be part of a UE 12. For uplink, atransmitter may be part of a UE 12 and a receiver may be part of a basestation 11. There is no limitation in the multiple access method appliedto a wireless communication system. Diverse methods can be used,including CDMA (Code Division Multiple Access), TDMA (Time DivisionMultiple Access), FDMA (Frequency Division Multiple Access), OFDMA(Orthogonal Frequency Division Multiple Access), SC-FDMA (SingleCarrier-FDMA), OFDM-FDMA, OFDM-TDMA, OFDM-CDMA. Uplink transmission anddownlink transmission can use either TDD (Time Division Duplex), whichuses different time locations for transmissions, or FDD (FrequencyDivision Duplex), which uses different frequencies for transmissions.

The layers of a radio interface protocol between a UE and a BS may beclassified as a first layer (L1), a second layer (L2), and a third layer(L3), based on three low layers of an Open System interconnection (OSI)model, which is well known in association with a communication system. Aphysical layer belonging to the L1 among the layers, provides aninformation transfer service using a physical channel.

A physical layer is connected to a media access control (MAC) layercorresponding to an upper layer through a transport channel. Data istransferred between the MAC layer and the physical layer through thetransport channel. The transport channel is classified based on a methodused to transport data through a radio interface. Further, data istransferred between different physical layers, for example, between aphysical layer of a user equipment (UE) and a physical layer of an eNBthrough a physical channel. The physical channel may be modulated usingan orthogonal frequency division multiplexing (OFDM) method and uses, asradio resources, a time, a frequency, and a space generated with aplurality of antennas.

FIG. 2 and FIG. 3 are diagrams schematically illustrating a structure ofa Radio Frame (RF) according to one or more exemplary embodiments. FIG.2 illustrates a concept of a D2D communication based on a cellularnetwork, and FIG. 3 illustrate an exemplary structure of configuring D2Ddiscovery resources.

Referring to FIG. 2 and FIG. 3, a radio frame may include ten subframes.A single subframe includes two slots. A time (a length) in which asingle subframe is transmitted is referred to as a Transmission TimeInterval (TTI). Referring to FIG. 2, for example, a length of a singlesubframe (1 subframe) may be 1 ms, and a length of a single slot (1slot) may be 0.5 ms.

A single slot may include a plurality of symbols in a time domain. Forexample, in a wireless system that uses Orthogonal Frequency DivisionMultiple Access (OFDMA) in a Downlink (DL), the symbol may be anOrthogonal Frequency Division Multiplexing (OFDM) symbol and in awireless system that uses Single Carrier-Frequency Division MultipleAccess (SC-FDMA) in an Uplink (UL), the symbol may be an SC-FDMA symbol.An expression associated with a symbol period of the time domain may notbe limited by a multiple access scheme or name.

The number of symbols included in a single slot may be different basedon a length of a Cyclic Prefix (CP). For example, in the case of anormal CP, seven symbols are included in a single slot, and in the caseof an extended CP, six symbols are included in a single slot.

A Resource Element (RE) may be the smallest unit of a time-frequencyresource to which a modulated symbol of a data channel, a modulatedsymbol of a control channel, or the like is mapped, and is a resourcecorresponding to a single symbol in the time domain and a singlesubcarrier in the frequency domain. A Resource Block (RB) is a resourceallocation unit, and may be a time-frequency resource corresponding to180 kHz in a frequency axis and a single slot in a time axis. Theresource block may be referred to as a Physical Resource Block (PRB). Aresource block pair refers to a resource block unit that includes twoconsecutive slots in a time axis.

Various physical channels may be used at a physical layer, and thephysical channels (data corresponding to the physical channels) may bemapped to the radio frame and transmitted. As a downlink physicalchannel, PDCCH (Physical Downlink Control Channel)/EPDCCH (EnhancedPDCCH) informs a UE of a resource allocation of Paging Channel (PCH) andDownlink Shared Channel (DL-SCH) and information of Hybrid AutomaticRepeat reQuest (HARQ) associated with DL-SCH. PDCCH/EPDCCH transfers anuplink grant, which informs a UE of a resource allocation of an uplinktransmission. PDCCH and EPDCCH are different with respect to mappingresource regions. Physical DL-SCH is mapped to Downlink Shared Channel(PDSCH). Physical Control Format Indicator Channel (PCFICH) informs a UEof the number of OFDM symbols used for PDCCH, and is transmitted inevery subframe. Physical Hybrid ARQ Indicator Channel (PHICH) is adownlink channel and transfers an HARQ ACK (Acknowledgement)/NACK(Non-acknowledgement) signal, which is a response to an uplinktransmission. HARQ ACK/NACK signal may be referred to as HARQ ACKsignal.

As an uplink physical channel, Physical Random Access Channel (PRACH)transfers a random access preamble. Physical Uplink Control Channel(PUCCH) transfers uplink control information, such as HARQ ACK as aresponse to a downlink transmission, Channel State Information (CSI) toindicate a channel state of a downlink channel, e.g., Channel QualityIndicator (CQI), Precoding Matrix Index (PMI), Precoding Type Indicator(PTI), Rank Indicator (RI), and the like. Physical Uplink Shared Channel(PUSCH) transfers Uplink Shared Channel (UL-SCH), which is a datachannel associated with control information of the PUCCH.

Uplink data may be transmitted on a PUSCH, and the uplink data may be atransport block (TB) that is a data block for a UL-SCH transmittedduring a transmission time interval (TTI). The TB may include user data.Further, the uplink data may be multiplexed data. In the multiplexeddata, the TB for the UL-SCH and uplink control information may bemultiplexed. That is, when user data to be transmitted through an uplinkis present, the UL control information may be multiplexed together withthe user data and be transmitted through the PUSCH.

Recently, a method of supporting D2D communication that uses atransmission and reception technology of a wireless communication systemin a frequency band of the wireless communication system or a bandexcluding the frequency band, and in this instance, enables user data tobe directly transmitted and received between devices, for example, UEswithout using an infrastructure, for example, an eNB, is inconsideration. The D2D communication enables wireless communication tobe available in an area outside of a limited wireless communicationinfrastructure and may also decrease network load of the wirelesscommunication system. Also, the D2D communication may transmitdisaster-related information to UEs even in a situation in which eNBsare not in normal operation due to, for example, a war and a disaster.

A UE to transmit a signal based on D2D communication is defined as atransmit UE (Tx UE) and a UE to receive a signal based on D2Dcommunication is defined as a receive UE (Rx UE). The Tx UE may transmita discovery signal and the Rx UE may receive the discovery signal. Rolesof the Tx UE and the Rx UE may be switched. A signal transmitted fromthe Tx UE may be received by at least two Rx UEs. Also, signalstransmitted by two or more Tx UEs may be selectively received by asingle Rx UE. A D2D signal may be transmitted through an uplinkresource. Therefore, a D2D signal may be mapped on an uplink subframeand may be transmitted from a Tx UE to an Rx UE. The Rx UE may receive aD2D signal on an uplink subframe.

FIG. 4 illustrates an example of D2D communication based on a cellularnetwork according to one or more exemplary embodiments.

Referring to FIG. 4, a cellular communication network including a firsteNB 410, a second eNB 420, and a first cluster 430 is configured. Afirst UE 411 and a second UE 412 located in a cell covered by the firsteNB 410 perform communication through a general connection link, forexample, a cellular link through the first eNB 410, which corresponds toan in-coverage-single-cell D2D communication scenario. The first UE 411located in a coverage of the first eNB 410 performs D2D communicationwith a fourth UE 421 located in a coverage of the second eNB 420, whichcorresponds to an in-coverage-multi-cell D2D communication scenario.Also, a fifth UE 431 out of the network coverage may generate a singlecluster, for example, the first cluster 430 together with a sixth UE 432and a seventh UE 433 and may perform D2D communication with the sixth UE432 and the seventh UE 433, which corresponds to an out-of-coverage D2Dcommunication scenario. The fifth UE 431 may operate as a cluster head(CH) of the first cluster 430. The cluster head may refer to a referenceUE, a node, or a unit, which serves as a reference for synchronizationpurpose, and assigns resources according to various purposes. Thecluster head may include an independent synchronization source (ISS) forsynchronizing out-of-coverage UEs. Further, a third UE 413 may performD2D communication with the sixth UE 432, which corresponds to apartial-coverage D2D communication scenario.

D2D communication may include direct communication in which D2D UEstransmit and receive data and control information for the purpose ofpublic safety. To support the D2D communication, a D2D discoveryprocedure and a D2D synchronization procedure may be executed. A D2Ddiscovery signal may be used solely for commercial purposes, forexample, advertizing or the like.

Related control information may be transmitted and received between UEsto perform D2D data transmission and reception through D2Dcommunication. The related control information may be referred to asscheduling assignment (SA). An Rx UE may perform a configuration for D2Ddata reception based on the SA. The SA may include at least one of, forexample, a new data indicator (NDI), a transmit UE identification (Tx UEID), a redundancy version (RV) indicator, a modulation and coding scheme(MCS) indication, a resource allocation (RA) indication, and a powercontrol indication.

Here, the NDI indicates whether a current transmission is repetition ofdata, that is, retransmission of the data or new data transmission. Areceiver may combine the same data based on the NDI. A target IDindicates an ID for a UE to which a corresponding data MAC PDU is to betransferred. The data MAC PDU may be transmitted through group castingor broadcasting based on the ID value, and may be transmitted eventhrough uni-casting based on the settings.

The RV indicator indicates a redundancy version by specifying differentstart points in a circular buffer for reading an encoded buffer. The TxUE may choose different redundancy versions about repetition of the samepacket based on the RV indicator. The MCS indication indicates an MCSlevel for D2D communication. The RA indication, e.g., transmissionresource pattern indication, indicates a time/frequency physicalresource allocated to transmit corresponding D2D data. The power controlindication may be a command for controlling a magnitude of power to besuitable for a UE having receiving corresponding data to performcorresponding D2D transmission.

From the perspective of a Tx UE, the Tx UE may operate in two modes forresource allocation.

Mode 1 refers to a case in which an eNB or a relay node (hereinafter,the eNB may include the relay node) schedules a predeterminedresource(s) for D2D communication. That is, in Mode 1, a predeterminedresource(s) used for transmitting D2D data and D2D control information(SA) of the Tx UE is designated by the eNB or the relay node. Mode 2refers to a case in which a predetermined resource(s) is selecteddirectly from a resource pool. That is, in Mode 2, the Tx UE maydirectly allocate a predetermined resource(s) for transmitting D2D dataand D2D control information.

A UE capable of performing D2D communication (“D2D capable UE”) supportsat least Mode 1 for in-coverage D2D communication. The D2D capable UEsupports at least Mode 2 for out-of-coverage D2D communication oredge-of-coverage D2D communication.

In the case of mode 1, a location of a resource(s) for transmission ofD2D control information and a location of a resource(s) for transmissionof D2D data, may be given by a Base Station (BS). That is, when anidentical grant for D2D SA and data transmission is given to a UE fromthe BS, by transmitting a (E)PDCCH in a DCI message format having a sizeidentical to that of DCI format 0.

In the case of mode 2, a resource pool for transmission of D2D controlinformation (e.g., SA) may be pre-configured and/or may besemi-statically allocated. In this instance, a Tx UE may select aresource for D2D control information from the resource pool, fortransmission of the D2D control information.

D2D discovery may be executed on a D2D discovery resource. For example,a D2D UE may transmit a discovery signal through a discovery resource(hereinafter referred to as a D2D discovery resource) that is randomlyselected (outside a network coverage) or is configured by a BS (inside anetwork coverage), with in a corresponding discovery period. In the caseof random selection, the resource for transmission of a discovery signalmay be determined, based on a fixed or adaptive transmission probabilityobtained from a pre-configured or configured normal transmissionprobability.

FIG. 5 is a diagram illustrating an example of a D2D discovery resourceaccording to an exemplary embodiment.

Referring to FIG. 5, a single D2D discovery resource may be formed of ncontiguous PRBs in the frequency domain and a single subframe. In thisinstance, inter-slot frequency hopping is not executed in the subframe.n may be, for example, 2 or 3.

A set of D2D resources (hereinafter referred to as a ‘D2D resource set’)may be used for repeated transmission of a Medium Access ControlProtocol Data Unit (MAC PDU) that delivers a discovery signal(hereinafter referred to as a discovery MAC PDU) within a discoveryperiod.

FIG. 6 is a diagram illustrating an example of a D2D discovery resourceset according to an exemplary embodiment.

Referring to FIG. 6, a D2D discovery resource set within a discoveryperiod may include contiguous D2D discovery resources or non-contiguousD2D discovery resources, in the time domain. That is, repeated D2Ddiscovery resources in the D2D discovery resource set may be contiguousor non-contiguous in the time domain.

FIG. 7 is a diagram illustrating examples of a D2D discovery resourceconfiguration structure in a D2D discovery resource set according to anexemplary embodiment.

Referring to FIG. 7, patterns indicate resources included in each D2Ddiscovery resource set. A plurality of D2D discovery resource sets mayexist in a single discovery period, and D2D discovery resources in asingle D2D discovery resource set may be contiguous (a) ornon-contiguous (b) in the time domain, and may be arranged in thefrequency domain based on frequency hopping (inter-subframe frequencyhopping). From the perspective of an Rx UE, a discovery signal may bemonitored within a resource pool for D2D reception. The resource poolfor D2D reception may be in a form of a super set, when compared to aresource pool for D2D transmission.

A definition of a discovery period may be different based on a discoverytype, that is, discovery type 1 and discovery type 2B. In the case oftype 1, the discovery period indicates the periodicity of resourcesallocated for D2D discovery signal transmission within a cell. In thecase of type 2B, the discovery period indicates the periodicity ofresources for the reception of a D2D discovery signal from a cell.Multiple discovery periods having various lengths may be used. In thecase of type 2B, a network may configure a predetermined resource fortransmission of a D2D discovery signal.

To determine whether to transmit a D2D discovery signal, a D2D discoverytransmission probability may be set.

A D2D UE that executes D2D discovery signal transmission may randomlyselect resources and transmits a discovery MAC PDU within a discoveryperiod. In this instance, the UE may not transmit a discovery MAC PDU inevery discovery period, but may determine a resource through which adiscovery MAC PDU is to be transmitted. The UE may determine a resourcethrough which a discovery MAC PDU is to be transmitted, based on a D2Ddiscovery transmission probability. The UE selects discovery resourcesin a discovery resource set within a set discovery period, randomly(type 1) or based on settings of a network (type 2), and transmits adiscovery MAC PDU (repeatedly) on the selected discovery resources.

For example, the D2D discovery transmission probability may bedetermined based on a period/offset. That is, what number is a discoverperiod in and a time/frequency offset are given, the UE may transmit aD2D discovery signal at a corresponding point.

As another example, the D2D discovery transmission probability may bebased on a fixed probability or an adaptive probability. (1) When it isbased on the fixed probability, whether to transmit a D2D discoverysignal on a discovery resource may be determined based on a randomfunction including a probability value P. (2) When it is based on theadaptive probability, this case may be similar to the case based on thefixed probability but the probability value P may adaptively vary. Forexample, when D2D discovery signal transmission is not executed in aprevious period, the probability value P may increase by k, and when D2Ddiscovery signal transmission is executed, the probability value P mayincrease by m. Alternatively, the probability value P may increasegradually, and may decrease by a predetermined value when apredetermined condition is satisfied.

In an exemplary embodiment, it is assumed that a D2D synchronizationSignal (D2DSS) and a Physical D2D Synchronization Channel (PD2DCH) arelocated in a resource that is configured by a network or a resourcedetermined in advance, so as to effectively support D2D discovery or D2Dcommunication. Therefore, when a D2DSS or a PD2DSCH is located in aresource for D2D discovery or D2D communication (SA/data), a D2D signaland a Wide Area Network (WAN) signal may be multiplexed in thecorresponding resource. Alternatively, a D2D synchronization signal anda D2D synchronization channel may be multiplexed with other signals,independently. The WAN refers to a network that configures a widecoverage in a cellular network and provides mobile UEs with voice/datatraffic, and the WAN includes WCDMA, LTE, WiMAX, and the like. Radioaccess networks are generally referred to as a WAN.

FIGS. 8 to 12 are diagrams illustrating delivery of information amongUEs and a BS, for D2D communication, according to an exemplaryembodiment. As an example, FIGS. 8 to 12 are flowcharts in associationwith resource configuration and transmission/reception of signals amonga BS, a D2D TxUE, and a D2D RxUE, in associated with D2D discoverysignal and data communication.

FIG. 8 is a diagram illustrating a process in which an idle mode UEexecutes transmission/reception of type 1 D2D discovery, in a wirelesscommunication system according to an exemplary embodiment.

Referring to FIG. 8, a TxUE and an RxUE obtain information associatedwith a TX/RX resource pool from a BS through an SIB, in operations 810and 812. The TxUE and the RxUE are in an idle mode, the BS broadcastsSIB information so as to provide the information associated with aresource pool for D2D communication.

The TxUE determines discovery transmission in operation 820, and selectsa discovery resource of a predetermined time/frequency domain for thediscovery transmission, based on the obtained information associatedwith the resource pool, in operation 830. The discovery resource may beselected based on a random function, and this may be identified based onidentification information of the UE.

The TxUE transmits a discovery signal through the selected discoveryresource in operation 840. The RxUE receives the discovery signal inoperation 850. This may be referred to as discovery type 1.

FIG. 9 is a diagram illustrating a process in which an RRC connectedmode UE executes transmission/reception of type 1 D2D discovery, in awireless communication system according to an exemplary embodiment.

When the UE has an RRC connection, type 1 discovery may be set through adedicated RRC signaling, and a BS may indicate corresponding resourcepool information.

Referring to FIG. 9, RRC connected mode TxUE and RxUE request type 1discovery transmission grant from the BS, in operations 900 and 902. TheBS determines a discovery grant request received from each UE, andgrants the request based on context of a corresponding UE, in operations905 and 907.

In this instance, the BS transmits configuration information associatedwith type 1, information associated with a Tx/Rx resource pool, and thelike through a dedicated signaling, to each of the RRC connected modeTxUE and RxUE, in operations 910 and 912. The TxUE and the RxUE are inan RRC connected mode, and the BS may transmit, to each UE, an RRCsignaling that includes configuration information for D2D discovery inRRC configuration information.

Subsequently, the TxUE determines discovery transmission in operation920, and selects a discovery resource of a predetermined time/frequencydomain for the discovery transmission, based on the obtained informationassociated with the resource pool, in operation 930. The discoveryresource may be selected based on a random function, and this may beidentified based on identification information of the UE. The TxUEtransmits a discovery signal through the selected discovery resource inoperation 940. The RxUE receives the discovery signal in operation 950.Here, FIG. 9 illustrates a process in which discovery type 1 isexecuted.

FIG. 10 is a diagram illustrating another example of transmitting andreceiving type 2B D2D discovery in an RRC connected mode, in a wirelesscommunication system according to an exemplary embodiment.

Referring to FIG. 10, D2D discovery type 2B is executed in an RRCconnected mode. The D2D discovery type 2B is executed in only an RRCconnected mode.

As an example, the BS transmits information associated with type 2 andinformation associated with a Tx/Rx resource pool for Type 2, through adedicated signaling, to each of the RRC connected mode TxUE and RxUE, inoperations 1010 and 1012. As a matter of course, the BS may allowexecution of type 2B discovery, based on whether a corresponding UE iscapable of executing type 2B discovery, or in response to a request froma UE.

Accordingly, the TxUE determines discovery transmission in operation1020, and selects/determines a discovery resource of a predeterminedtime/frequency domain, which is configured through the dedicatedsignaling in operation 1030.

Therefore, the TxUE transmits a discovery signal through only theconfigured discovery resource in operation 1040. The RxUE receives thediscovery signal in operation 1050. Here, FIG. 10 illustrates a processin which discovery type 2 is executed.

FIG. 11 is a diagram illustrating another process in which D2D datacommunication is executed in an RRC connected mode, in a wirelesscommunication system according to an exemplary embodiment.

FIG. 11 illustrates a process of executing mode 2 ProSe directcommunication before executing mode 2 communication in an RRC connectedmode. As an example, the mode 2 operation may be used for an exceptionalcase such as RLF, and mode 1 operation may be executed as the default.An idle mode UE executes the mode 2 operation based on informationindicated by the SIB.

Particularly, the RRC connected mode TxUE and RxUE request ProSe directcommunication transmission grant from a BS, in operations 1100 and 1102The BS determines the ProSe direct communication transmission grantreceived from each UE, and grants the request based on context of acorresponding UE, in operation 1105 and 1107.

The BS transmits configuration information associated with mode 2 andinformation associated with a Tx/Rx resource pool for mode 2, through adedicated signaling, to each of the RRC connected mode TxUE and RxUE, inoperations 1110 and 1112. The TxUE and the RxUE are in an RRC connectedmode, the BS may transmit, to each UE, an RRC signaling that includesinformation for the mode 2 D2D data communication in RRC configurationinformation.

The TxUE determines communication transmission in operation 1120, andselects/determines a resource for communication (SA/data), based on theobtained/configured resource pool information, in operation 1130.

Subsequently, the TxUE transmits communication SA/data through theselected resource, in operation 1140. The RxUE receives thecommunication data in operation 1150.

FIG. 12 is a diagram illustrating another process in which D2D datacommunication is executed in an RRC connected mode, in a wirelesscommunication system according to an exemplary embodiment.

FIG. 12 illustrates a process of executing mode 1 ProSe directcommunication before executing mode 1 communication in an RRC connectedmode.

Particularly, the RRC connected mode TxUE and RxUE request ProSe directcommunication transmission grant from a BS, in operations 1200 and 1202The BS determines the ProSe direct communication transmission grantreceived from each UE, and grants the request based on context of acorresponding UE, in operations 1205 and 1207.

The BS transmits configuration information associated with mode 1 andinformation associated with a Tx/Rx resource pool for mode 1, through adedicated signaling, to each of the RRC connected mode TxUE and RxUE, inoperations 1210 and 1212. The TxUE and the RxUE are in an RRC connectedmode, the BS may transmit, to each UE, an RRC signaling that includesinformation for the mode 1 D2D data communication in RRC configurationinformation.

The TxUE determines communication transmission in operation 1220, andreports a buffer state associated with the D2D data through a ProSe BSRin operation 1224. The BS that receives the ProSe BSR from the TxUE mayallocate a ProSe SA/ProSe data grant for D2D data transmission. TheProSe SA/ProSe data grant may be indicated through a PDCCH or an EPDCCH,in operation 1228.

The TxUE that obtains the ProSe SA/ProSe data grant selects/determines aresource for communication (SA/data) based on the configured resourcepool information and the SA/data grant, in operation 1230.

The TxUE transmits ProSe SA/ProSe data (communication data) through theselected resource, in operation 1240. The RxUE receives thecommunication SA/data in operation 1250.

When a plurality of D2D signals overlap temporally with respect to asingle UE, a collision may occur among the D2D signals. However, anexisting UE, particularly, a UE having a single transceiver chain, isincapable of executing simultaneous transmissions/receptions throughvarious frequency bands. Accordingly, for effective D2D communication ina licensed band, there is a need of assigning a priority a signal forprocessing D2D signals when a collision occurs among the D2D signals.

Accordingly, an exemplary embodiment will provide a method ofmultiplexing D2D signals when a plurality of D2D signals occurssimultaneously. Particularly, a method for a UE having a singletransceiver chain to execute multiplexing D2D signals, will bedescribed. Hereinafter, the methods disclosed in an exemplary embodimentmay be applicable to a multi-carrier scenario. For example, an exemplaryembodiment may be applied to multiplexing of a UE that has a singletransceiver chain on a cellular spectrum (carrier #0) and an uplinkspectrum (on FDD) for D2D.

A D2D signal may include a D2D discovery signal and a D2D communicationsignal. The D2D discovery signal may be classified into type 1 and type2B. A type 1 D2D discovery signal is transmitted on a resource that israndomly selected from a D2D discovery resource set, and a type 2B D2Ddiscovery signal is transmitted on a resource that is configured bysettings of a network. The D2D communication signal may include SA andD2D data. SA transmission for D2D communication may be indicated by aDCI format having a size identical to DCI format 0 in the case of mode1, and may be indicated using a resource randomly selected randomly froma SA resource pool in the case of mode 2.

Here, the SA resource pool may be configured in advance in anout-of-coverage D2D communication scenario, and may be indicated by anSIB/dedicated signaling in an in-coverage/partial-coverage D2Dcommunication scenario. Alternatively, it may be fixed to apredetermined location. For example, it may be fixed to a predeterminedlocation in a resource pool for D2D data transmission.

D2D data is indicated by SA in the both cases, that is, mode 1 and mode2. A Resource Pattern for Transmission (RPT) may be used for D2D datatransmission. In this instance, a pattern for a time domain resource isreferred to as a T-RPT, and a pattern for a frequency domain resource isreferred to as an F-RPT. However, indication associated with thefrequency domain resource may be determined or indicated by apredetermined hopping pattern.

FIG. 13 illustrates an example of a potential collision among D2Dsignals. FIG. 13 assumes a single carrier scenario. FIG. 14 illustratesan example of a potential collision among D2D signals. FIG. 14 assumes amulti-carrier scenario.

As shown in FIGS. 13 and 14, a collision may occur between a D2Ddiscovery signal and D2D data (or SA) on a single carrier, or acollision may occur between D2D data (or SA) of a carrier and SA (or D2Ddata) of another carrier. In the case of D2D discovery and D2Dcommunication, a transmission timing may not be controlled by a singlenetwork. For example, for reception of an inter-PLMN discovery signal, acorresponding UE may monitor reception of a discovery signal transmittedon another PLMN (or carriers), during a predetermined period of time. Inparallel with the above, D2D signal transmission or reception may occuron a serving PLMN (or carriers).

In this instance, a method of multiplexing D2D signals when a pluralityof D2D signals are simultaneously generated, according to an exemplaryembodiment, will be described as follows.

Before applying the methods of the following embodiments, a D2Dsynchronization signal and a D2D synchronization channel may execute D2Dtransmission with a higher priority than other D2D channels. That is, itindicates that the D2D synchronization signal and the D2Dsynchronization channel may be preferentially transmitted when theyoverlap temporally or collide with another D2D discovery channel, a D2Dcontrol channel (SA), or a D2D data channel, and other D2D channels maynot be transmitted or puncturing of partial information thereof may beexecuted. Particularly, when the D2D synchronization signal collideswith a D2D control channel (SA)/data channel, puncturing may be executedwith respect to OFDM symbols that overlap the D2D synchronization signalin a subframe through which the D2D control channel is transmitted, andthe D2D control channel/data channel may be transmitted together withthe D2D synchronization signal. Conversely, when the D2D synchronizationchannel is transmitted and the D2D synchronization channel collides withother D2D channels, the other D2D channels may not be transmitted. Here,the case of not being transmitted may not indicate all transmissionsincluding retransmission of a D2D channel, but may indicate only atransmission of a D2D channel when a collision occurs.

A method of assigning priorities of the D2D channels remaining afterexcluding the D2D synchronization signal and the synchronizationchannel, will be described as follows.

According to an exemplary embodiment, when a collision occurs among D2Dsignals, a final priority may be determined by combining maximumtransmission power level (e.g., Pmax) information in settings of aresource pool configured for a D2D discovery channel and a priority thatis based on a channel mentioned in the first embodiment. The maximumtransmission power information in the settings for the D2D discoverychannel resource pool may be classified as three power levels, that is,maximum/medium/minimum level. Also, the D2D data transmission power mayindicate a maximum power or a general open loop power control, based ona TPC command. Accordingly, D2D data transmission to which a maximumpower is set may also be considered. Therefore, by taking intoconsideration a power level of each channel, a channel having a highpower has a high priority. When maximum transmission power informationof channels that collide are identical to each other, the final prioritymay be determined in an order of a discovery signal>SA>data according tothe first embodiment. A D2D channel having the highest priority may bepreferentially transmitted, and remaining channels may be dropped ortransmitted through puncturing.

For example, when transmission of a D2D discovery signal (maximumpower), a D2D SA signal (maximum power), and D2D data (medium power,open loop power control) occurs on a single carrier with respect to asingle UE that executes D2D, a D2D data channel that has a medium powerlevel is dropped first according to the above described method, and aD2D discovery signal is finally transmitted out of the D2D discoverysignal and the D2D SA signal having the maximum power, based on apriority item of the corresponding channels.

According to the first embodiment, when a collision occurs among D2Dsignals, a priority may be assigned in an order of a discoverysignal>SA>data, and D2D transmission may be executed based on the same.In this instance, as a main consideration, a discovery signal may have along transmission period (for example, few seconds), and a delay inreception of a D2D discovery signal may be prevented by receiving a D2Ddiscovery signal preferably within a single discovery period.

For example, when transmission/reception of a discovery signal occurs inparallel with transmission/reception of SA, the transmission/receptionof the discovery signal is always prioritized over thetransmission/reception of the SA. Therefore, the method may beconsidered as a method that prioritizes the transmission/reception of adiscovery signal.

According to the first embodiment, when a discovery Tx signal and an SATx signal are generated in parallel on the same subframe, the SA Txsignal may be dropped. A transmission period of the discovery signal islonger than general D2D communication (SA, data) signals and thus, notmissing a discovery signal in a discovery period is important.Therefore, according to the first embodiment, a delay intransmission/reception of a discovery signal may be minimized.

Additionally, when identical D2D signals collide on different carriers(PLMNs or cells), a D2D signal corresponding to a serving cell (or PLMN)may be preferentially transmitted or received.

According to a second embodiment, whether a D2D signal is a Tx signal oran Rx signal is considered to determine a priority. In this instance,whether a D2D signal is a Tx/Rx may be considered as a more importantelement or a type of D2D signal may be considered as a more importableelement, to set a priority. For example, the priority may be set in anorder of a discovery Tx>SA Tx>data Tx>discovery Rx>SA Rx>data Rx. Asanother example, the priority may be set in an order of a discoveryTx>discovery Rx>SA Tx>SA Rx>data Tx>data Rx.

According to the second embodiment, transmission (or reception) of apredetermined D2D signal may be more prioritized than transmission (orreception) of another signal. The second embodiment is based on thepriority of the first embodiment. Here, the meaning of ‘being based onthe priority of the first embodiment’ is that the priority is determinedby considering the feature of a D2D signal based on the first embodimentand considering whether a type of the D2D signal is a Tx/Rx according tothe second embodiment when events with an identical priority exists.This also means that the priority of the second embodiment is consideredfirst and, when events with an identical priority exists, considerationsof the first embodiment may be used, to determine a priority.Alternatively, the priority may be determined irrespective of thepriority of the first embodiment.

A third embodiment determines priorities of D2D signals based on atleast one of a D2D communication mode and a discovery type.

Particularly, the priorities of the D2D signals may be determined basedon D2D communication mode 1/2 and D2D discovery type 1/2B. For example,the priority may be determined in an order of type 2B discovery>mode 1SA>mode 1 data>type 1 discovery>mode 2 SA>mode 2data. The embodiment isa method of determining a priority based on at least one of a D2D signaltransmission mode and a D2D signal type. A type 2B discovery signal istransmitted using a resource designated by a network. Therefore, usingthe resource for the signal may be preferentially requested. Also, whenthe frequency of transmission of the signal is considered together, thetype 2B discovery signal may be a D2D signal having the highestpriority. Similarly, SA of mode 1 is a resource that is also designatedbased on a DCI of a network, and thus, may have a high priority.

In addition to the embodiments, a fourth embodiment regards a D2D signalthat is temporally earlier as a signal with a higher priority, whenmultiple carriers are configured for a UE. The method may determine D2Dresources configured on multiple carriers, and may determine a prioritybased on the same. The fourth embodiment may be optionally considered.

The first to fourth embodiments are exclusive, and one of theembodiments may be used or at least one of the embodiments may be usedtogether. For example, by combining the third embodiment and the secondembodiment, the following priority may be obtained. For example, type 2Bdiscovery Tx/Rx>mode 1 SA Tx/Rx>mode 1 data Tx/Rx>type 1 discoveryTx>mode 2 SA Tx>mode 2 data Tx>type 1 discovery Rx>mode 2 SA Rx>mode 2data Rx.

What is meant here is that a condition of one of the mentioned fourembodiments is considered first, and when events with an identicalpriority exists, a condition of another embodiment may be considered.Therefore, the intention is to enable a UE to determine final prioritiesof corresponding D2D signals.

According to the method according to an exemplary embodiment, when a UEhas a single transceiver chain, a signal having a low priority may bedropped. This may be equally applied to a single carrier environment ormulti-carrier environment.

Alternatively, even in the case where the UE has an independenttransceiver chain, when D2D signals are simultaneously generated onmultiple carriers and the transmission power of the D2D signals exceedP_(CMAX) that is a maximum output power configured for the UE (a totalconfigured maximum output power), the D2D signals may be selectivelydropped or power scaling may be executed (for example, decreasing Txpower) based on a priority. Power scaling refers to reduction of atransmission power based on a predetermined scale, so as to allocatepower that does not exceed a total transmission power of a UE. Anexample of power scaling is multiplexing an original transmission powerby a scaling factor. The power scaling may be expressed variously, suchas power adjustment, power-scale down, or the like. That is, accordingto an exemplary embodiment, D2D signals are distinguished based on apriority and power scaling may be selectively executed.

FIG. 15 is an example of a flowchart illustrating operations of a UEaccording to an exemplary embodiment.

Referring to FIG. 15, the UE determines whether a collision occurs amongD2D signals in operation S1500. That is, it is determined whether acollision occurs since a plurality of D2D signals are set or scheduledto be simultaneously transmitted/received in an identicalspectrum/subframe.

When the collision occurs, the UE determines priorities of the pluralityof D2D signals, so as to determine a D2D signal to be processed, inoperation S1510. The UE may determine the priorities for determining asignal to be processed (or transmitted/received) out of the plurality ofD2D signals, and executes multiplexing, based on at least one of thefirst to the fourth embodiments.

As an example, the priority may be determined based on a type of D2Dsignal, for example, in an order of a discovery signal>SA>data.

As another example, the priority may be determined based on whether aD2D signal is a Tx signal or an Rx signal.

As another example, the priority may be determined based on at least oneof a D2D communication mode and a discovery type.

As another example, a D2D signal that is temporally earlier than othersignals may be regarded as a signal with a higher priority. Thiscorresponds to the case in which multiple carriers are configured forthe UE.

When D2D signals colliding into each other have the same priority inassociation with the priority considered first out of the abovedescribed examples, another priority out of the remaining examples maybe considered. Therefore, the above mentioned priority examples may besequentially considered.

Based on the determination, the UE transmits or receives a D2D signalwith a high priority, which is selected out of the plurality of D2Dsignals based on the priority, in operation S1520. Also, when the D2Dsignals are simultaneously generated on the multiple carriers and thetransmission power of the D2D signals exceed a P_(CMAX), the UE may(selectively) drop the D2D signals or execute power scaling based on thepriority.

FIG. 16 is an example of a block diagram illustrating a UE according toan exemplary embodiment.

Referring to FIG. 16, a UE 1600 includes a UE transmitting unit 1605, aUE receiving unit 1610, and a UE processor 1620. The UE may furtherinclude a memory (not illustrated). The memory is connected with the UEprocessor 1620, and store various pieces of information used foroperating the UE processor 1620. In the above described embodiments, theoperations of the UE 1600 may be implemented by a control of theprocessor 1620. The UE processor 1620 may further include a collisiondetermining unit 1625 and a multiplexing unit 1630.

The UE transmitting unit 1605 executes transmission of a D2D signal.

The UE receiving unit 1610 executes reception of a D2D signal.

The collision determining unit 1625 may determine whether a collisionoccurs since a plurality of D2D signals are set or scheduled to besimultaneously transmitted/received in an identical spectrum/subframe.

The multiplexing unit 1630 may determine the priorities of the pluralityof D2D signals so as to decide a signal to be processed in acorresponding spectrum/subframe, and execute multiplexing, based on atleast one of the first to the fourth embodiments. The multiplexing unit1630 may be referred to as a scheduling unit in respect that the unitschedules a signal to be transmitted/received, may be referred to as apriority determining unit in respect that the unit determines thepriorities of the D2D signals colliding into each other, and may bereferred to as a selecting unit in respect that the unit selects asignal to be processed out of the plurality of D2D signals.

For example, the multiplexing unit 1630 may determine the priorities ofthe D2D signals having a collision, in an order of a discoverysignal>SA>data.

As another example, the multiplexing unit 1630 may determine thepriorities of the D2D signals having a collision, based on whether a D2Dsignal is a Tx signal or an Rx signal.

As another example, the multiplexing unit 1630 may determine thepriorities of the D2D signals having a collision, based on at least oneof a D2D communication mode and a discovery type.

As another example, the multiplexing unit 1630 may determine a D2Dsignal that is temporally earlier as a signal with a higher prioritythan other signals. This corresponds to the case in which multiplecarriers are configured for the UE 1600.

The UE processor 1620 may further include a power controller (notillustrated). The power controller may determine whether D2D signals aresimultaneously generated on the multiple carriers and the transmissionpower for the D2D signals exceed P_(CMAX), and when the transmissionpower for the D2D signals exceed P_(CMAX), the power controller mayexecutes power scaling (selectively) with respect to the D2D signalsbased on a priority.

A BS 1650 includes a BS receiving unit 1655, a BS transmitting unit1660, and a BS processor 1670. The BS 1650 may further include a memory(not illustrated). The memory is connected with the BS processor 1670,and stores various pieces of information used for operating the BSprocessor 1670. In the above described embodiments, the operations ofthe BS 1650 may be implemented by a control of the processor 1670. TheBS processor 1670 may include an RRC connection determining unit 1675, aD2D resource allocation unit 1680, and a D2D mode setting unit 1685.

The BS transmitting unit 1655 may transmit D2D configuration informationto the UE 1600.

The RRC connection determining unit 1675 may determine whether the UE1600 is in an idle mode or an RRC connected mode. The D2D mode settingunit 1685 may set a D2D mode of the UE 1600.

The D2D resource allocation unit 1680 may generate informationassociated with a resource pool for D2D communication, based on whetherthe UE 1600 is in an idle mode or an RRC connected mode. Also, the D2Dresource allocation unit 1680 may generate D2D configurationinformation. The D2D configuration information may include configurationinformation associated with a D2D discovery type 1/type 2, informationassociated with a corresponding Tx/Rx resource pool, and the like. TheD2D configuration information may include information associated with aD2D resource pool for D2D mode2/mode 1. A monitoring resource associatedwith D2D discovery reception may be configured in a form of a subset,which is smaller than or equal to the D2D discovery resource pool. TheD2D configuration information may include information associated with aD2D monitoring period (monitoring resource information). The monitoringresource information may include only information associated with aperiod where D2D signals of D2D UEs that access a network of a singleoperator is monitored, or may include information associated with aperiod where D2D signals of D2D UEs that access the network of thesingle operator is monitored and information associated with a periodwhere D2D signals of D2D UEs that access a network of another operatoris monitored.

According to an exemplary embodiment, a Tx UE may include a wirelesstransceiver (not shown). The UE receiving unit 1610 and the UEtransmitting unit 1605 may be configured as a single wirelesstransceiver or a separate wireless transceivers. In an exemplaryembodiment, the term “wireless transceiver” may be used to describe oneof the above communication units or transceivers.

The wireless transceiver may receive resource assignment informationtransmitted from an evolved NodeB (eNB) and transmit a D2D discoverysignal to a Rx UE. The resource assignment information may be associatedwith a D2D discovery signal to be transmitted in a discovery period.

One or more processors, e.g., the UE processors 1620, may be configuredto determine that a D2D discovery signal associated with a firstdiscovery type and a D2D discovery signal associated with a seconddiscovery type are to be transmitted in a first subframe included in thediscovery period. The one or more processors may be configured to, inthe first subframe, transmit the D2D discovery signal associated withthe second discovery type and drop the D2D discovery signal associatedwith the first discovery type.

The first discovery type may correspond to discovery type 1 for a D2Ddiscovery signal transmission, and the second discovery type maycorrespond to discovery type 2B for a D2D discovery signal transmission.The wireless transceiver may be configured to receive information ofresource pool for a D2D discovery signal transmission associated withthe discovery type 1, and the one or more processor may be configured torandomly select a transmission resource within the resource pool toexecute the D2D discovery signal transmission associated with thediscovery type 1.

The wireless transceiver may be configured to receive information ofdedicated discovery resource for a D2D discovery signal transmissionassociated with the discovery type 2B, the information of dedicateddiscovery resource being transmitted from the eNB, and the wirelesstransceiver may be configured to execute the D2D discovery signaltransmission associated with the discovery type 2B using the dedicateddiscovery resource.

The wireless transceiver may be configured to transmit the D2D discoverysignal associated with the first discovery type in a second subframe inresponse to determining, by the one or more processors, that the D2Ddiscovery signal associated with the second discovery type is notscheduled for transmission in the second subframe, wherein the secondsubframe is included in the discovery period.

The one or more processor may be configured to drop a D2D control signaltransmission in response to determining that a D2D discovery signal andthe D2D control signal are to be transmitted in a second subframe. Inthe second subframe, the wireless transceiver may be configured totransmit the D2D discovery signal without transmitting the D2D controlsignal, wherein the second subframe is included in the discovery period.

The one or more processor may be configured to drop a D2D data signaltransmission in response to determining that a D2D discovery signal andthe D2D data signal are to be transmitted in a second subframe. In thesecond subframe, the wireless transceiver is configured to transmit theD2D discovery signal without transmitting the D2D data signal, whereinthe second subframe is included in the discovery period.

According to an exemplary embodiment, the wireless transceiver of the TxUE may receive configuration information for a D2D communication from aneNB, and receive information of a resource pool transmitted from theeNB. The information of the resource pool may be associated with a firstD2D discovery signal transmission. Further, the wireless transceiver mayreceive discovery resource information associated with a second D2Ddiscovery signal transmission, the discovery resource informationindicating a specific resource for the second D2D discovery signaltransmission. The one or more processors of the UE may determine thesecond D2D discovery signal transmission through the specific resource,the specific resource comprising a first subframe and a second subframe.The one or more processors of the UE may determine the first D2Ddiscovery signal transmission through a resource selected from theresource pool, the selected resource comprising the second subframe anda third subframe. Then, the one or more processors may execute thesecond D2D discovery signal transmission in the second subframe, anddrop the first D2D discovery signal transmission in the second subframe.

The first D2D discovery signal transmission may be associated withdiscovery type 1, and the second D2D discovery signal transmission maybe associated with discovery type 2B. The one or more processors mayexecute the second D2D discovery signal transmission in the firstsubframe. The one or more processors may determine that the second D2Ddiscovery signal transmission is not executed in the third subframe, andexecute the first D2D discovery signal transmission in the thirdsubframe.

In the described exemplary system, although methods are described basedon a flowchart as a series of steps or blocks, aspects are not limitedthereto. It is understood that the specific order or hierarchy of stepsin the processes disclosed is an illustration of exemplary approaches.Based on design preferences, it is understood that the specific order orhierarchy of steps in the processes may be rearranged. Further, somesteps may be combined or omitted. The accompanying method claims presentelements of the various steps in a sample order, and are not meant to belimited to the specific order or hierarchy presented.

The previous description is provided to enable any person skilled in theart to practice the various aspects described herein. Variousmodifications to these aspects will be readily apparent to those skilledin the art, and the generic principles defined herein may be applied toother aspects. Thus, the claims are not intended to be limited to theaspects shown herein, but is to be accorded the full scope consistentwith the language claims, wherein reference to an element in thesingular is not intended to mean “one and only one” unless specificallyso stated, but rather “one or more.” Unless specifically statedotherwise, the term “some” refers to one or more. All structural andfunctional equivalents to the elements of the various aspects describedthroughout this disclosure that are known or later come to be known tothose of ordinary skill in the art are expressly incorporated herein byreference and are intended to be encompassed by the claims. Moreover,nothing disclosed herein is intended to be dedicated to the publicregardless of whether such disclosure is explicitly recited in theclaims. No claim element is to be construed as a means plus functionunless the element is expressly recited using the phrase “means for.”

What is claimed is:
 1. A method of a device-to-device (D2D)communication between user equipments (UEs), the method comprising:receiving, at a transmission (Tx) UE, resource assignment informationtransmitted from an evolved NodeB (eNB), the resource assignmentinformation being associated with a D2D discovery signal to betransmitted in a discovery period; determining, at the Tx UE, that a D2Ddiscovery signal associated with a first discovery type and a D2Ddiscovery signal associated with a second discovery type are to betransmitted in a first subframe included in the discovery period; in thefirst subframe, transmitting the D2D discovery signal associated withthe second discovery type and dropping the D2D discovery signalassociated with the first discovery type; and transmitting the D2Ddiscovery signal associated with the first discovery type in a secondsubframe in response to determining that the D2D discovery signalassociated with the second discovery type is not scheduled fortransmission in the second subframe, wherein the second subframe isincluded in the discovery period.
 2. The method of claim 1, wherein: thefirst discovery type corresponds to discovery type 1 for a D2D discoverysignal transmission; and the second discovery type corresponds todiscovery type 2B for a D2D discovery signal transmission.
 3. The methodof claim 2, further comprising: receiving, at the Tx UE, information ofresource pool for a D2D discovery signal transmission associated withthe discovery type 1; and randomly selecting a transmission resourcewithin the resource pool to execute the D2D discovery signaltransmission associated with the discovery type
 1. 4. The method ofclaim 2, further comprising: receiving, at the Tx UE, information ofdedicated discovery resource for a D2D discovery signal transmissionassociated with the discovery type 2B, the information of dedicateddiscovery resource being transmitted from the eNB; and executing the D2Ddiscovery signal transmission associated with the discovery type 2Busing the dedicated discovery resource.
 5. The method of claim 1,further comprising: determining, at the Tx UE, that a D2D discoverysignal and a D2D control signal are to be transmitted in a thirdsubframe; and in the third subframe, transmitting the D2D discoverysignal and dropping the D2D control signal, wherein the third subframeis included in the discovery period.
 6. The method of claim 1, furthercomprising: determining, at the Tx UE, that a D2D discovery signal and aD2D data signal are to be transmitted in a third subframe; and in thethird subframe, transmitting the D2D discovery signal and dropping theD2D data signal, wherein the third subframe is included in the discoveryperiod.
 7. A transmission (Tx) user equipment (UE) to execute adevice-to-device (D2D) communication with a reception (Rx) UE, the Tx UEcomprising: a wireless transceiver configured to: receive resourceassignment information transmitted from an evolved NodeB (eNB), theresource assignment information being associated with a D2D discoverysignal to be transmitted in a discovery period; and transmit a D2Ddiscovery signal to a Rx UE; and one or more processors configured to:determine that a D2D discovery signal associated with a first discoverytype and a D2D discovery signal associated with a second discovery typeare to be transmitted in a first subframe included in the discoveryperiod; and in the first subframe, determine to transmit the D2Ddiscovery signal associated with the second discovery type and to dropthe D2D discovery signal associated with the first discovery type,wherein the wireless transceiver is configured to transmit the D2Ddiscovery signal associated with the first discovery type in a secondsubframe in response to determining, by the one or more processors, thatthe D2D discovery signal associated with the second discovery type isnot scheduled for transmission in the second subframe, wherein thesecond subframe is included in the discovery period.
 8. The Tx UE ofclaim 7, wherein: the first discovery type corresponds to discovery type1 for a D2D discovery signal transmission; and the second discovery typecorresponds to discovery type 2B for a D2D discovery signaltransmission.
 9. The Tx UE of claim 8, wherein the wireless transceiveris configured to receive information of resource pool for a D2Ddiscovery signal transmission associated with the discovery type 1, andthe one or more processor is configured to randomly select atransmission resource within the resource pool to execute the D2Ddiscovery signal transmission associated with the discovery type
 1. 10.The Tx UE of claim 8, wherein the wireless transceiver is configured toreceive information of dedicated discovery resource for a D2D discoverysignal transmission associated with the discovery type 2B, theinformation of dedicated discovery resource being transmitted from theeNB, and wherein the wireless transceiver is configured to execute theD2D discovery signal transmission associated with the discovery type 2Busing the dedicated discovery resource.
 11. The Tx UE of claim 7,wherein the one or more processor is configured to drop a D2D controlsignal transmission in response to determining that a D2D discoverysignal and the D2D control signal are to be transmitted in a thirdsubframe, and wherein in the third subframe, the wireless transceiver isconfigured to transmit the D2D discovery signal without transmitting theD2D control signal, wherein the third subframe is included in thediscovery period.
 12. The Tx UE of claim 7, wherein the one or moreprocessor is configured to drop a D2D data signal transmission inresponse to determining that a D2D discovery signal and the D2D datasignal are to be transmitted in a third subframe, and wherein in thethird subframe, the wireless transceiver is configured to transmit theD2D discovery signal without transmitting the D2D data signal, whereinthe third subframe is included in the discovery period.
 13. A method ofa device-to-device (D2D) communication between user equipments (UEs),the method comprising: receiving, at a transmission (Tx) UE, resourceassignment information transmitted from an evolved NodeB (eNB), theresource assignment information being associated with a D2D discoverysignal to be transmitted in a discovery period; determining, at the TxUE, that a D2D discovery signal associated with a first discovery typeand a D2D discovery signal associated with a second discovery type areto be transmitted in a first subframe included in the discovery period;in the first subframe, transmitting the D2D discovery signal associatedwith the second discovery type and dropping the D2D discovery signalassociated with the first discovery type; determining, at the Tx UE,that a D2D discovery signal and a D2D control signal are to betransmitted in a second subframe; and in the second subframe,transmitting the D2D discovery signal and dropping the D2D controlsignal, wherein the second subframe is included in the discovery period.14. The method of claim 13, further comprising: determining, at the TxUE, that a D2D discovery signal and a D2D data signal are to betransmitted in a third subframe; and in the third subframe, transmittingthe D2D discovery signal and dropping the D2D data signal, wherein thethird subframe is included in the discovery period.
 15. The method ofclaim 13, further comprising: transmitting the D2D discovery signalassociated with the first discovery type in a third subframe in responseto determining that the D2D discovery signal associated with the seconddiscovery type is not scheduled for transmission in the third subframe,wherein the third subframe is included in the discovery period.
 16. Amethod of a device-to-device (D2D) communication between user equipments(UEs), the method comprising: receiving, at a transmission (Tx) UE,resource assignment information transmitted from an evolved NodeB (eNB),the resource assignment information being associated with a D2Ddiscovery signal to be transmitted in a discovery period; determining,at the Tx UE, that a D2D discovery signal associated with a firstdiscovery type and a D2D discovery signal associated with a seconddiscovery type are to be transmitted in a first subframe included in thediscovery period; in the first subframe, transmitting the D2D discoverysignal associated with the second discovery type and dropping the D2Ddiscovery signal associated with the first discovery type; determining,at the Tx UE, that a D2D discovery signal and a D2D data signal are tobe transmitted in a second subframe; and in the second subframe,transmitting the D2D discovery signal and dropping the D2D data signal,wherein the second subframe is included in the discovery period.
 17. Themethod of claim 16, further comprising: determining, at the Tx UE, thata D2D discovery signal and a D2D control signal are to be transmitted ina third subframe; and in the third subframe, transmitting the D2Ddiscovery signal and dropping the D2D control signal, wherein the thirdsubframe is included in the discovery period.
 18. The method of claim16, further comprising: transmitting the D2D discovery signal associatedwith the first discovery type in a third subframe in response todetermining that the D2D discovery signal associated with the seconddiscovery type is not scheduled for transmission in the third subframe,wherein the third subframe is included in the discovery period.